Compare Ionic, Polar, and Non-polar Bonds


Ionic Bonding:

The formation of an Ionic bond is the result of the transfer of one or more electrons from a metal onto a non-metal.

Covalent Bonding:

Bonding between non-metals consists of two electrons shared between two atoms. In covalent bonding, the two electrons shared by the atoms are attracted to the nucleus of both atoms. Neither atom completely loses or gains electrons as in ionic bonding.

There are two types of covalent bonding:

1. Non-polar bonding with an equal sharing of electrons.

2. Polar bonding with an unequal sharing of electrons. The number of shared electrons depends on the number of electrons needed to complete the octet.

Comparison of Ionic, Polar and Non-Polar Bonding:

Whereas non-polar bonding involves the equal sharing of electrons between identical non-metal atoms, POLAR BONDING is the unequal sharing of electrons between two different non metal atoms. A proper understanding of polar bonding is gained by viewing the types of bonding on a continuum. Ionic bonding is on one extreme with a complete transfer of electrons forming charged ions. Non-polar covalent bonding with equal sharing of electrons is at the other extreme. Somewhere in the middle but favoring the covalent side is polar bonding with unequal sharing of electrons and partial but incomplete transfer of electrons.

Comparison of Lewis Diagrams of Ionic, Polar and Non-Polar Bonding:

The best way to show and represent the unequal sharing of electrons would be by comparison with NaCl and HCl, and H2 using Lewis diagrams.

The captions below correspond to the graphic on the right.

IONIC: Complete transfer of electrons, therefore Na becomes positive (lost e-) and Cl becomes negative (gained e-).

POLAR: Unequal sharing. Chlorine has a greater tendency to keep its own electron and also draw away hydrogen's electron. It is NOT completely successful. As a result only partial charges are established. Hydrogen becomes partially positive since it has lost control of its electron some of the time (H +). Chlorine becomes partially negative since it gains hydrogen's electron some of the time (Cl -).

 In summary, a polar bond results when different atoms share electrons. One atom will attract the bonding electrons more strongly than the other atom and will acquire more than a half share of these electrons. This leaves the other atom with less than a half share and makes the electron distribution unsymmetrical. On a time-average basis the electrons spending more time with one atom cause it to have a partial negative charge. The other atom deficient in electrons acquires a partial positive charge.

NON-POLAR: Equal Sharing. Neither atom can dominate the other, therefore the electrons are shared equally between them.